[meta] New releases should post notifications in resolved issues/merged PRs

# 🚀 Feature request
When a new release is published, it includes information in the changelog about which PRs are included and which issues are fixed in the new version. The publishing process should include automated notification hooks so that those following the issues/PRs will see the message and know that it's resolved.

I'm making an issue for this per [this comment](https://github.com/angular/angular-cli/issues/13212#issuecomment-457889697) from @IgorMinar.

Empieza por rastrear el proceso de publicación de releases que genera entradas del changelog para los PRs incluidos y los issues corregidos. Determina dónde podrían añadirse hooks de notificación y qué eventos de issues y pull requests de GitHub deben actualizar; se considera terminado cuando una release publicada notifica automáticamente a los seguidores de los elementos referenciados.

Escrito por el modelo de indexación a partir del texto del issue.